The present invention relates to a gas-blast load-break switch and, more particularly, to a breaker switch including a negative pressure generating apparatus for forming blasting gas flow against an arc.
A conventional gas-blast load-break switch of disclosed in, for example, U.S. Pat. No. 4,511,776, comprises a sealed container containing arc extinguishing fluid such as SF.sub.6 gas or the like and disconnectable fixed and contacts, with a pressure storage device including a pressure storage chamber for raising the pressure of arc extinguishing fluid using the arc energy generated by the separation of those contacts and with a negative pressure generating device including a negative pressure chamber generating negative pressure by the relative movement between a cylinder and a piston caused by the separating operation of the movable contact. With the above described construction, the arc between the detached contacts will be extinguished by a blasting of gas flow directed from the pressure storage chamber to the negative pressure chamber, which gas flow is caused by the differential pressure between the initial pressure and rising pressure caused by the arc energy in the pressure storage chamber and the negative pressure in the negative pressure chamber.
In the abovementioned prior art, the contact length L is predetermined between the movable contact and the fixed contact when the movable contact is thrown into the fixed contact, with the length L being equal to the length of the piston movement defining the negative pressure chamber. Consequently, the movable contact moves by the distance L relative to the fixed contact during the breaking operation of the movable contact, the movable contact begins to be detached from the fixed contact and, at the same time, the negative pressure chamber initiates to communicate with the gas chamber located on the other side of the negative chamber from the piston. Subsequently, the negative pressure chamber immediately communicates with the gas chamber on the other side thereof from the piston.
In this case, therefore, the pressure by the arc energy cannot be satisfactorily raised to achieve a complete extinguishing of the arc. For example, when an electric current of approximately 100 to 500 ampere is applied between the contacts, as the electric current being relatively lower, the arc is extinguished by merely the differential pressure between the initial pressure in the pressure storage chamber and the negative pressure in the negative pressure chamber. Further, when a higher electric current is applied between the contacts, the rising pressure caused by the arc energy in the pressure storage chamber instantly risen because the arc energy is generated in proportion to the higher current, thereby extinguishing the arc. However, for example, when the contacts are subjected to an high-intensity electric current to approximately 1000 to 3000 ampere, the rising pressure produced by the arc energy in the pressure storage chamber is not sufficient. Therefore, a problem arises in that the arc generated between the contacts cannot be extinguished by the insufficient differential pressure between the initial pressure and rising pressure caused by the arc energy in the pressure storage chamber and the negative pressure in the negative pressure chamber.
Furthermore, according to the abovementioned prior art, the volume of the gas chamber on the opposite side of the piston from the negative pressure chamber is smaller than that of the pressure storage chamber and the negative pressure chamber, which gas chamber is filled up with the heated fluid after extinguishing the arc. As a result, a further problem arises in that the temperature of the arc extinguishing fluid in the gas chamber is raised to an extent that insulating capacity of the arc extinguishing fluid itself is remarkably deteriorated and loses its insulating ability.